Problem: At the moment a hot cake is put in a cooler, the difference between the cake's and the cooler's temperatures is $50\degree$ Celsius. This causes the cake to cool and the temperature difference loses $\dfrac15$ of its value every minute. Write a function that gives the temperature difference in degrees Celsius, $D(t)$, $t$ minutes after the cake was put in the cooler. $D(t)=$
Explanation: If $\dfrac{1}{5}$ of the temperature difference is lost each minute, that means $\dfrac{4}{5}$ of the difference remains each minute. So each minute, the temperature difference is multiplied by a factor of $\dfrac{4}{5}$ (or $0.8$ ). If we start with the initial temperature difference, $50\degree$ Celsius, and keep multiplying by $\dfrac{4}{5}$, this function gives us the temperature difference $t$ minutes after the cake was put in the cooler: $D(t)=50\left(\dfrac{4}{5}\right)^t$